High iodobromide tabular grain silver halide emulsions with {111} crystallographic faces are known to provide an improved balance of sensitivity and granularity along with improved image sharpness as described in U.S. Pat. No. 4,439,520 (Kofron et al). The predominately iodobromide emulsions described in this patent, however, are slow to develop and can be difficult to adequately bleach and fix when employed in color forming elements.
Attempts have been made to provide emulsions exhibiting all the desirable characteristics described in the noted patent, particularly excellent photographic sensitivity, while simultaneously providing improved developability and improved bleaching and fixing behavior by replacing some or all of the bromide and iodide ion of these emulsions with chloride ion. These early high chloride emulsions required the presence of a substituted hydrocarbon grain growth modifier to both enable growth of the morphologically unstable {111} form and to stabilize that grain form once present.
Nevertheless, these emulsions still suffered from a lack of morphological stability that limited their commercial utility because the emulsion dependent photographic properties would change drastically over time. Subsequently, attempts at providing high chloride {111} tabular emulsions have focused on improved grain growth modifiers and methods of morphological stabilization by providing various organic compounds that serve to better direct grain growth towards {111} tabular forms and to stabilize the grain surface as described, for example, in U.S. Pat. No. 5,176,991 (Jones), U.S. Pat. No. 5,176,992 (Maskasky) or U.S. Pat. No. 4,952,491 (Nishikawa et al). The first two patents do not have any specific teaching about preferred color development methods while the last one teaches the use of developer solutions containing little or no bromide ion.
While the grain growth control and morphological stability of the high chloride {111} tabular emulsions has been greatly advanced by these techniques, those emulsions with well-adhered organic surface stabilizer when coated in a photographic element still prove difficult to adequately develop and desilver, while those emulsions with poorly adhered or purposefully removed organic surface stabilizer still suffer from morphological instability. More recently, it has been reported in U.S. Pat. No. 5,035,992 (Houle et al), that improved morphological stability can be achieved with high chloride {111} grains of various morphologies by the expedient of incorporating a bromide or iodide band. Additional examples of bromide or iodide stabilized {111} high chloride tabular grain emulsions are illustrated in U.S. Pat. No. 5,217,858 (Maskasky) and U.S. Pat. No. 5,389,509 (Maskasky). The emulsions described in these patents still require the presence of a grain growth modifier to ensure formation of the {111} faced tabular shaped grains. Further, the application of these emulsions to camera speed color negative films is not described.
The use of specific developer formulations to provide rapid access has likewise been investigated. Cubic silver chloride emulsion grains again specifically precipitated with organic grain growth modifiers and described as corner development grains (CDGs) are disclosed in U.S. Pat. No. 4,820,624 (Hasebe et al) and U.S. Pat. No. 4,865,962 (Hasebe et al). When properly sensitized these symmetric CDG emulsions are said to provide improved sensitivity. Here, the developer solution employed to provide rapid access contains no restraining bromide ion. EP-A-0,468,780 (published 29 Jan. 1992) describes low bromide ion developer formulations said to be useful with color negative films employing cubic silver bromochloride emulsions. Although rapid development using a low bromide developer is described, the overall light sensitivity of these films is severely deficient. Further, it is taught in U.S. Pat. No. 5,354,649 (Bell et al) that the quantity of bromide in these emulsions is such as to lead to rapid deactivation of the developer solution employed as bromide ion washes out of the film and into the developer solution during a development step.
Cubic shaped silver chloride emulsions and useful development methods are disclosed in EP-A-0,466,417 (published 15 Jan. 1992), and in Japanese Kokai 04-101135 (published 2 Apr. 1992). Rapid access is apparently obtained in a low bromide color developer solution but only with relatively light insensitive emulsions unsuitable for use in a hand-held camera.
Other low bromide developer solutions suitable for color papers employing low sensitivity regular shaped high chloride emulsions are disclosed in U.S. Pat. No. 5,004,675 (Yoneyama et al), U.S. Pat. No. 5,066,571 (Yoshida et al), U.S. Pat. No. 5,070,003 (Naruse et al), U.S. Pat. No. 5,093,226 (Ohshima), U.S. Pat. No. 5,093,227 (Nakazyo et al), U.S. Pat. No. 5,108,877 (Asami), U.S. Pat. No. 5,110,713 (Yoshida et al), U.S. Pat. No. 5,110,714 (Furusawa et al), U.S. Pat. No. 5,118,592 (Hasebe), U.S. Pat. No. 5,153,108 (Ishikawa et al) and U.S. Pat. No. 5,162,195 (Inagaki). These publications teach that low quantities of bromide ion in the developer variously improve staining and pressure fog characteristics. Concentrations of bromide ion between about 0.05 mmol/l and about 1 mmol/l are described as optimal while bromide ion concentrations greater than about 1 mmol/l are discouraged since these are said to reduce sensitivity of the regular shaped emulsions. Additionally, higher quantities of bromide ion in a developer intended for low to no bromide ion containing high chloride regular shaped emulsions are known to lead to incorporation of bromide ion from the developer into undeveloped portions of the emulsion during a development step. This incorporation, known as metathesis, results in two related problems, that is the depletion of bromide ion from the developer which must then be replenished more often than typically desired and incorporation of the bromide ion into emulsion which must then be removed during a desilvering step where silver bromide is well known to be more difficult to remove than is silver chloride.
The continuing problem of providing rapidly developable camera speed color photographic elements is well expressed in U.S. Pat. No. 5,344,750 (Fujimoto et al) at column 1 (lines 35ff) where it is stated that "the high chloride emulsions used in color paper can be rapidly developed in comparison with silver halide emulsions containing silver iodide used in color negative films for photography, but sufficiently high sensitivity can not be obtained and hence the high silver chloride emulsions can not be used in the color negative films for photography." The use of highly light sensitive silver iodobromide emulsions in a camera speed film that is then processed at elevated temperatures in highly concentrated developing agent and bromide ion containing developer solutions is suggested as a means of resolving this long standing problem. The higher temperatures and otherwise tightly controlled developer solution composition required by this approach are difficult to provide especially since continuous processing leads to a steady decrease in developing agent and developer bromide ion concentration that results in unwanted degrees of fog growth. Further, the higher levels of iodide ion in the emulsions remove the possibility of ready and rapid desilvering with environmentally suitable agents. Thus, this proposal hardly fits with the public desire for the use of ecologically benign film process solutions.
Yet another means of resolving these difficulties is proposed in U.S. Pat. No. 5,354,649 (Bell et al) where the bromide ion content of the light sensitive emulsions and the developer solution are both said to be critical to the sensitivity issue and the developability issue. This patent proposes that photographic materials employing cubic silver iodochloride emulsions comprising only very limited quantities of bromide ion, when developed in a very low to no bromide ion developer solution can provide rapidly developable films of somewhat improved sensitivity. The desilvering problems inherent in high iodide emulsion elements are however still present. In an attempt to provide both normal development and rapid development with a common film element it is proposed in U.S. Pat. No. 5,382,501 (Inoie) that multilayer, multicolor camera speed elements employing specific twin-grain AgIBr emulsions where the iodide content of the emulsions employed in a more sensitive and a less sensitive blue light sensitive layers, is controlled within a narrow range can provide blue color unit gamma that is relatively insensitive to inverse changes in both development time and temperature.
All of these proposals fail in that, one or another requirement for a successful rapid access camera speed film and process is not met. Either camera speed in not attainable with the emulsions proposed or adequate gamma in the various color records to enable color printing is not achieved, or the emulsions are unstable, or the process proposed is inherently unstable or the processing schemes proposed result in a situation where the various color units disposed at differing physical depths in a multilayer multicolor film develop at differing rates and result in a wide spread in color unit developability and gamma thereby detracting from the utility of the formed image.
Thus a need still exists to provide a camera speed color element suitable for rapid access color development as well as a means of processing such a film element that enables even development throughout the various color records and further provides for rapid and complete desilvering of such an element.